Experiments will be continued in an effort to determine the mechanism of activation of latent fatty acid synthetase (FAS) in livers of starved or newly-hatched chicks in response to feeding. Latent enzyme is defined as enzyme activity which is not measured in vitro under optimum assay conditions but which can be measured after in vivo activation (in response to feeding) or after suitable in vitro manipulations which result in apparent activation of inactive enzyme. Attempts will be made to characterize and quantitate various forms of FAS in chick liver by affinity chromatography. Studies will also be conducted to determine if the increase of lipogenesis resulting from Hg treatment of biotin-deficient chicks is the result of an increase of absolute amount of acetyl-CoA carboxylase (ACC) in liver. Immunochemical techniques will be used to quantitatively precipitate ACC. BIBLIOGRAPHIC REFERENCES: Liou, G. I. and W. E. Donaldson (1977) Avian fatty acid synthetase: evidence for short-term regulation of activity. Arch. Biochem. Biophys. 178: 195-199. Donaldson, W. E. (1977) Selenium inhibition of avian fatty acid synthetase complex. Chemico-Biol. Interactions, in press.